The wireless communication system has evolved to broadband wireless communication systems (e.g., 3rd generation partnership project (3GPP) high speed packet access (HSPA) and long term evolution (LTE or evolved universal terrestrial radio access (E-UTRA)) and 3GPP2 high rate packet data (HRPD), ultra-mobile broadband (UMB), and institute of electrical and electronics engineers (IEEE) 802.16e that are capable of providing high-speed, high-quality wireless packet data communication services beyond the early voice-oriented services.
The LTE system, as one of the representative broadband wireless communication systems, uses orthogonal frequency division multiplexing (OFDM) in the downlink and single carrier frequency division multiple access (SC-FDMA) in the uplink. Such a multiple access scheme is characterized by allocating the time-frequency resources for transmitting user-specific data and control information without overlap of each other, i.e., maintaining orthogonality, so as to distinguish among user-specific data and control information.
The LTE system adopts a Hybrid Automatic Repeat Request (HARQ) scheme for physical layer retransmission when decoding failure occurs in initial data transmission. The HARQ scheme is designed to operate in such a way that a receiver that fails in decoding data sends a transmitter a negative acknowledgement (NACK) indicative of decoding failure in order for the transmitter to retransmit the corresponding data on the physical layer. The receiver combines the retransmitted data with the decoding-failed data to improve data reception performance. It may also be possible for the receiver to send the transmitter an Acknowledgement (ACK) indicative of successful decoding, when the data are decoded successfully, in order for the transmitter to transmit new data.
An LTE system may be configured to support a low-cost low-complexity user equipment (UE) (hereinafter, interchangeably referred to as low-cost, MCE, or M2M UE) by limiting some UE functions. A low-cost UE is likely to be suitable for MTC and M2M services in the fields of remote meter reading, crime prevention, and distribution. The low-cost UE is expected to become a promising means for realizing cellular-based Internet of things (IoT).
In order to meet the low-cost/low-complexity requirements, the low-cost UE operating in a narrowband with a bandwidth narrower than that of the system transmission band may communicate with the eNB using some or all RBs. For example, the low-cost UE has a capability to transmit and receive signals on a narrow band channel of 1.4 MHz as the smallest system transmission bandwidth supported in LTE/LTE-A and thus always communicates with the eNB in the bandwidth of 1.4 MHz. Accordingly, the eNB may configure the low-cost UE for communication therewith in one of a plurality of narrowbands within the system transmission bandwidth.
The eNB may also configure the low-cost UE for narrowband communication therewith according to a predetermined frequency hopping pattern. A narrowband for use by the low-cost UE spans 6 resource blocks, and the system transmission bandwidth contains a plurality of resource blocks arranged without being overlapped with each other. Since the resource blocks for use by the low-cost UE should be aligned along with the resource blocks for use by the legacy UEs within the system transmission bandwidth, the resource blocks for use by the low-cost UEs and legacy UEs are identical with each other.
In order to meet the low-cost/low-complexity requirements, consideration may be given to reducing the RF device cost by decreasing the number of receive antennas of the UE to 1 or to reducing the data reception buffer cost by setting an upper limit of the transport block size (TBS) capable of being processed by the MTC UE. Unlike the normal LTE UE that has a wideband signal transmission/reception function at least in 20 MHz bandwidth regardless of the system transmission bandwidth, the low-cost MTC is configured to have a maximum bandwidth less than 20 MHz to contribute to the realization of low-cost/low-complexity. For example, it may be possible to define the operation of a low-cost UE operating in a maximum channel bandwidth of 1.4 MHz in the LTE system with the channel bandwidth of 20 MHz.
The low-cost UE may experience poor coverage at a certain location such as cell boundary and, for coverage enhancement of the low-cost UE, consideration is given to repetitive transmission and frequency hopping. The repetitive transmission and frequency hopping method may be used for coverage enhancement for a normal LTE UE. There is therefore a need of a channel estimation and data decoding method for the low-cost UE performing the repetitive transmission and frequency hopping in the coverage enhancement mode which is differentiated from the channel estimation and data decoding method for the legacy normal LTE UE without coverage degradation.
In order to meet the increasing demand for wireless data traffic since the commercialization of 4th generation (4G) communication systems, the development focus is on the 5th generation (5G) or pre-5G communication system. For this reason, the 5G or pre-5G communication system is called a beyond 4G network communication system or post long-term evolution (LTE) system. Consideration is being given to implementing the 5G communication system in millimeter wave (mmWave) frequency bands (e.g., 60 GHz bands) to accomplish higher data rates. In order to increase the propagation distance by mitigating propagation loss in the 5G communication system, discussions are underway about various techniques such as beamforming, massive multiple-input multiple output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large-scale antenna. Also, in order to enhance network performance of the 5G communication system, developments are underway of various techniques such as evolved small cell, advanced small cell, cloud radio access network (RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-points (CoMP), and interference cancellation. Furthermore, the ongoing research includes the use of hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM){FQAM} and sliding window superposition coding (SWSC) as advanced coding modulation (ACM), filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA), and sparse code multiple access (SCMA).
Meanwhile, the Internet is evolving from a human-centric communication network in which information is generated and consumed by humans to the Internet of things (IoT) in which distributed things or components exchange and process information. The combination of the cloud server-based Big data processing technology and the IoT begets Internet of everything (IoE) technology. In order to secure the sensing technology, wired/wireless communication and network infrastructure, service interface technology, and security technology required for implementing the IoT, recent research has focused on sensor network, machine-to-machine (M2M) communication, and machine-type communication (MTC) technologies. In the IoT environment, it is possible to provide an intelligent Internet Technology that is capable of collecting and analyzing data generated from connected things to create new values for human life. The IoT can be applied to various fields such as smart home, smart building, smart city, smart car or connected car, smart grid, health care, smart appliance, and smart medical service through legacy information technology (IT) and convergence of various industries.
Thus, there are various attempts to apply the IoT to the 5G communication system. For example, the sensor network, M2M communication, and MTC technologies are implemented by means of the 5G communication technologies such as beamforming, MIMO, and array antenna. The application of the aforementioned cloud RAN as a big data processing technology is an example of convergence between the 5G and IoT technologies.